1. Field of the Invention
The present invention relates to a compression encoder and a compression-encoding method by which first and second digital image signals having frame rates different from each other are compressed on the basis of an equal encoding method, and a recorder and a recording method by which digital image signals thus compressed are recorded onto a recording medium.
2. Description of the Related Art
In the past, there have been proposals for a VTR (Video Tape Recorder) capable of reproducing video signals recorded on recording media according to various formats and of further converting the signals into different formats (ref. Jpn. Pat. Appln. Laid-Open Publication No. 2-171090). In this conventional VTR, the operation state can be changed automatically based on the system of video signals to be reproduced and that of video signals to be set. Determination of the recorded television system can be made by measuring the field frequency.
On the other hand, in recent years, practical use of television systems according to digital systems has been promoted, and broadcasting systems have been diversified. Therefore, a multi-format-compatible VTR for broadcasting use which is compatible with plural formats has been proposed. This multi-format-compatible VTR is compatible with progressive scanning in which every frame consists of one field and HD (Hi Definition) system, in addition to NTSC and PAL, as suggested in the Publication No. 2-171090.
A signal processor suggested in Jpn. Pat. Appln. Laid-pen Publication No. 2001-285802 has been proposed as a VTR of the multi-format-compatible type. In this signal processor, operation modes of a system converter which performs P/I conversion (Progressive-scanning/Interlace-scanning conversion) and I/P (Interlace-scanning/Progressive-scanning conversion) conversion can be automatically changed on the basis of reproduction format information recorded on a magnetic tape and output format information instructed in advance, in order to record/reproduce both of 480I (480 lines and interlace scanning) and 480P (480 lines and progressive scanning).
Also in this signal processor, displacement of the barycenter between first and second fields forming one frame can be eliminated by performing a vertical filtering processing on video signals to be outputted, when reproduction at a changed speed such as ½-speed reproduction in which the tape speed of reproduction is half the speed of recording is performed, for example, in the format of 480I.
However, in the conventional signal processor, suppose a case that recording is performed in a different format for every frame rate (30 and 60 frames/second) in the 4:2:2 format which is based on four luminance blocks and two color difference signal blocks for each of Cb and Cr. In this case, if the frame rate of 60 frames/second is subjected to ½-speed reproduction as described above, an interpolation processing is required and the resolution hence deteriorates. Also, in the conventional signal processor described above, decoders need to be developed respectively for the different formats, in order to achieve an optimal reproduction operation for each format. There has been a problem that the development period is prolonged in addition to increase in development costs of the whole signal processor.
Also in the 4:2:2 format, reproduction processing can be executed by one single decoder if recording has been carried out in the format at the frame rate of 30 frames/second. However, if recording has been carried out in the other format at the frame rate of 60 frames/second, two decoders are required. The format at 60 frames/second can be equivalent to the format at 30 frames/second in reproduction by executing the ½-speed reproduction as described above. However, shuffling methods for rearranging macro blocks in accordance with formats are different between both of the formats. Therefore, two decoders are finally required for reproduction, resulting in a problem that labor saving in developments and speed-up of reproduction processings cannot progress. Note that the same problem occurs in other encoding systems such as a 4:4:4 format and the like.